The present invention relates to an apparatus for continuously advancing and welding metal can bodies and the like and, more particularly, to an apparatus for continuously forming and laser welding metal can bodies.
The applicability of laser welding for fabricating can bodies is known. For example, in U.S. Pat. No. 4,152,573 to Saurin, et al., a method and apparatus for laser welding metal can bodies are disclosed. The article "The Laser Welding Of Steels Used In Can Making" by J. Mazumder and W. M. Steen, Welding Journal, June, 1981, pages 19-25, also discusses the advantages of laser welding in can making. However, the apparatus disclosed in these references for advancing and welding metal can bodies are not suitable for the type of continuous, high-speed operation necessary for production in most commercial applications. In particular, in each of these references the can body or metal being welded is fixedly clamped on both sides of the weld joint area by clamping bars of a vise or fixture. During welding the vise or fixture and the can body or metal sheet clamped therein are advanced relative to a laser welding device to accomplish the welding. Thus, with these known apparatus an individual metal sheet to be welded must be first clamped, then welded, and thereafter unclamped from the vise or fixture before a second metal sheet can be processed. Such an apparatus is not suitable for commercial applications where continuous, high rates of production, such as 400-600 cans per minute, are necessary or desirable.
The Z-bar guide apparatus disclosed in applicant's aforementioned U.S. Pat. Nos. 4,272,004 and 4,354,090 make it possible to position and guide the opposed edges of generally tubular shaped sheets of metal so that the sheets of metal may be continuously advanced and lap or butt welded to produce metal can bodies. To accomplish this a means for advancing the sheet material along the can forming machine through the Z-bar and past the welding station, must be provided. As indicated in the aforesaid patents, depending upon the type of conventional welder involved, conventional chain type conveyors, drive rollers, reciprocating pistons or push rods or the like may be used to advance the sheet material. However, it has been found that these conventional advancing mechanisms may be problematical or not applicable, especially in the case of continuous high-speed laser, electron beam or other noncontact welding of the metal can bodies. For example, with the use of conventional chain type conveyors having chains with fingers or dogs for engaging the metal sheets, there may be problems in accurately aligning the opposed edges of a metal sheet in the longitudinal direction, particularly at the high speeds possible when laser welding due to chain vibration and stretching of the chain because of the numerous joints and tolerances associated with such joints. A slight misalignment of the welded edges can result in difficulty in joining the ends of the can to the tubular metal body and/or possible leakage of the can in this area once the ends have been joined to the can body.
The conventional apparatus for advancing and welding metal can bodies may also be problematical where they require frequent starting and stopping of the can bodies as they are advanced along the machine to permit various operations such as, crimping of joints to be soldered. Where the metal can bodies are to be electrical resistance welded, the conventional apparatus may provide a high speed acceleration of the can bodies near the welding rollers to close the gaps between successive can bodies as they enter the nip of the resistance welding rollers thereby preventing the rollers from contacting each other. These abrupt changes in motion, e.g. starting and stopping or fluctuating the speed of the advancing can bodies immediately before welding may be problematical in that they require additional time for processing of the can bodies and/or can lead to jamming of the apparatus and the consequent time and expense associated with alleviating such a condition.
An object of the present invention is to provide an apparatus for continuously advancing and welding metal can bodies and the like which avoids the aforementioned disadvantages of the conventional apparatus. More particularly, an object of the present invention is to provide an apparatus for continuously forming and laser welding metal can bodies which is suitable for high-speed production, which advances successive generally tubular shaped sheets of metal so as to accurately align the opposed edges in the longitudinal direction, and which does so in a relatively smooth and efficient manner to minimize jamming problems and allow continuous welding with constant speed and constant power requirements.
These and other objects of the invention are attained by providing an apparatus for continuously forming and laser welding metal can bodies comprising forming means for successively forming flat sheets of metal into generally tubular shaped sheets of metal having longitudinally extending edges to be welded, advancing means for successively advancing the generally tubular shaped sheets of metal from the forming means to a first position in a direction toward a laser welding means such that the generally tubular shaped sheets of metal are moving at a predetermined speed at the first position, additional advancing means for continuously advancing the successive moving generally tubular shaped sheets of metal from the first position to a second position at a substantially constant speed, and laser welding means arranged for welding the longitudinally extending edges of the generally tubular shaped sheets of metal as they are advanced by the additional advancing means.
According to a disclosed, preferred embodiment of the apparatus of the invention, the additional advancing means includes a pair of endless metal belts extending between the first and second positions, each of the belts having a plurality of fingers mounted thereon in spaced relationship for engaging the trailing ends of successive generally tubular shaped sheets of metal to advance the sheets.
Means are provided for arranging the pair of metal belts in spaced relationship on opposite sides of the longitudinally extending edges to be welded. This means for arranging the metal belts includes guide roll means and drive sprocket means for supporting and driving the respective belts in spaced relationship, the drive sprocket means being provided with a plurality of teeth on their outer surfaces for drivingly engaging in a series of holes formed in the respective belts. According to one form of the invention the holes formed in the belts are rectangular in shape and the driving faces of the teeth on the driving sprocket means are flat for engaging a side of the rectangular holes to drive the belts. The apparatus also includes means for resiliently biasing at least one guide roll means supporting each belt to tension the belts.
The guide roll means and drive sprocket means support the metal belts in spaced relationship so that they move between the first and second positions in paths parallel to the paths of the respective portions of the successive sheets of metal which are engaged by the fingers on the belts. This reduces the wear on the fingers and damage to the sheet ends which would otherwise be caused by the transverse sliding of the fingers with respect to the trailing ends of the metal sheets.
Guide bar means are provided under each metal belt between the guide roll means and the driving sprocket means to prevent vibrations and vertical movement of the belts during operation of the apparatus. The guide bar means between the drive sprocket means and the adjacent guide roll means on the downstream side of the drive sprocket means includes stripper means adjacent the drive sprocket means for stripping the metal belts off the drive sprocket means. According to a preferred form of the invention the stripper means are knife edges formed of a wear resistant material.
The metal belts are preferably formed of stainless steel and have a thickness of from 0.005 to 0.020 inch. The fingers are connected to respective base plates and connecting means are provided for connecting the respective base plates to the metal belts. The connecting means connect each of the base plates to the belts along a single line along the length of the base plates which extends in a direction perpendicular to the direction of movement of the belts. This permits the base plates with fingers to move about the curved surfaces of the guide roll means and drive sprocket means without unduly stressing the belts. The connecting means according to a preferred form of the invention are rivets having caps which engage the belts. The surfaces of the rivet caps in contact with the belts are arcuate so that the base plates may pivot or rotate about the single line of connection with the belts during their movement about the guide roll means and the drive sprocket means.
The base plates of the fingers are formed within close tolerances to the same predetermined length and thickness before they are connected to the metal belts. In addition, guide bar means are provided for supporting the outer surfaces of the base plates as they advance the generally tubular shaped metal bodies between the first and second positions. These measures ensure that any canting or tilting of the base plates on the belts in response to stresses applied to the respective fingers in advancing the sheets of metal, is uniform thereby maintaining the precise longitudinal alignment of the opposed edges to be welded. The accuracy of the longitudinal positioning of the opposed edges to be welded is also enhanced according to the present invention in that the surfaces of the fingers on the belts which cooperate to engage the trailing end of a generally tubular shaped sheet of metal and advance the same are match-machined with respect to each other either before or after the base plates thereof have been connected on the belts. In a preferred form of the invention the fingers are formed of investment cast tool steel.
According to a further feature of the invention the advancing means for successively advancing the generally tubular shaped sheets of metal from a forming means to a first position in a direction toward a laser welding means includes indexing means for repeatedly moving successive generally tubular shaped sheets of metal over at least the distance between the forming means and the first position. The indexing means in one form of the invention includes a cam indexer. According to another form of the invention the indexing means includes a D.C. servomotor.
As an additional feature, the advancing means comprises a pair of endless chains extending between the forming means and the first position, each of the chains having a plurality of fingers mounted thereon for engaging the respective trailing ends of successive generally tubular shaped metal sheets to advance the sheets. The chains are arranged in spaced relationship on opposite sides of the generally tubular shaped sheets of metal and extend about respective drive sprockets and idler sprockets.
The apparatus further includes means for adjusting the distance between the respective drive sprockets and the distance between the respective idler sprockets. Means are also provided for adjusting the distance between the forming means and the idler and drive sprockets. These features permit the apparatus to be adjusted to advance and weld a wide range of sizes of generally tubular shaped sheets of metal. In this regard, as another feature of the invention, means are provided for adjusting the position of the forming means with respect to the advancing means so that the trailing ends of the generally tubular shaped sheets of metal may be positioned at the same location along the advancing means with a change in the length or height of the sheet metal or can body.
Thus, as a result of the invention an apparatus is provided for continuously advancing and welding metal can bodies and the like at high speeds with improved accuracy of alignment of the longitudinal edges to be welded. Moreover, the apparatus of the invention can be used to advance and weld a great variety of cans with wide ranging can diameters and heights. Further, with the apparatus of the invention the can bodies are moved by means of the indexing means from the forming means to a first position in a direction toward a welding means such that they are moving at a predetermined speed at the first position and thereafter the additional advancing means permits the successive shaped sheets of metal to be continuously advanced to a second position at a substantially constant speed for laser welding thereby reducing the likelihood of jamming of the apparatus and permitting relatively high production rates.
These and other objects, features and advantages of the present invention will become more apparent from the following description when taken in connection with the accompanying drawings which show, for purposes of illustration only, one preferred embodiment in accordance with the present invention.